In this paper, we have proposed speculative locking (SL) protocols to improve the performance of distributed database systems (DDBSs) by trading extra processing resources. In SL, a transaction releases the lock on th...
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In this paper, we have proposed speculative locking (SL) protocols to improve the performance of distributed database systems (DDBSs) by trading extra processing resources. In SL, a transaction releases the lock on the data object whenever it produces corresponding after-image during its execution. By accessing both before and after-images, the waiting transaction carries out speculative executions and retains one execution based on the termination (commit or abort) mode of the preceding transactions. By carrying out multiple executions for a transaction, SL increases parallelism without violating serializability criteria. Under the naive version of SL, the number of speculative executions of the transaction explodes with data contention. By exploiting the fact that a submitted transaction is more likely to commit than abort, we propose the SL variants that process transactions efficiently by significantly reducing the number of-speculative executions. The simulation results indicate that even with manageable extra resources, these variants significantly improve-the performance over two-phase locking in the DDBS environments where transactions spend longer time for processing and transaction-aborts occur frequently.
In this paper, the effects of two-phase locking on the performance of a distributed database management system are evaluated. In particular, the relationship between the average transaction response time for four conc...
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In this paper, the effects of two-phase locking on the performance of a distributed database management system are evaluated. In particular, the relationship between the average transaction response time for four concurrency control algorithms based on two-phase locking has been established with respect to the static degree of interference for a given multiprogramming level, database size, and transaction size. The increase in average probability of one lock request conflicting with another has been measured with respect to the static degree of interference and the percentage of aborted transactions has been measured for each algorithm. In addition, the impact of a number of parameters (e.g. data replication, lock predeclaration, time-out, local processing time, degree of locality of references, interarrival time, number of nodes and transmission time) on the performance of a distributed database management system in the presence of a concurrency control mechanism has also been measured. The study has been made using simulation and the SIMULA programming language.
The quality of fragments allocation is key for improving performance of join query in distributed database. Current strategies concentrate on using heuristic rules to allocate fragments to corresponding locations, suc...
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The quality of fragments allocation is key for improving performance of join query in distributed database. Current strategies concentrate on using heuristic rules to allocate fragments to corresponding locations, such as picking the location with maximum required data or with greedy algorithm. Notwithstanding their benefits, under distributed environment, facing various query plans, different data distributions and expensive network cost, their scene-sensitive character may easily generate low quality allocation plan due to lack of generalization ability. In this paper, for breaking this limitation, we propose a general strategy for allocating fragments(AlCo, Allocate fragments based on Cost). AICo evaluates multiple candidate allocation plans based on cost, which is realized by a modified genetic algorithm employed from PostgreSQL. Our fitness function (cost model) synthetically considers various changeable factors to support generalization ability. For reducing the risks caused by randomization of genetic algorithm, AICo provides an upper bound computed through current heuristic methods to improve the robustness of our genetic algorithm. We implement AICo in a distributed database system, and the experiments show that, on TPC-H benchmark, AICo is up to 2x-4x better on performance than existing strategies and performs well in robustness and scalability. (C) 2019 Elsevier Inc. All rights reserved.
High-performance low-cost PC hardware and high-speed LAN/WAN technologies make distributed database (DDB) systems an attractive research area where query optimization and DDB design are the two important and related p...
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High-performance low-cost PC hardware and high-speed LAN/WAN technologies make distributed database (DDB) systems an attractive research area where query optimization and DDB design are the two important and related problems. Since dynamic programming is not feasible for optimizing queries in a DDB, we propose a new genetic algorithm (GA)-based query optimizer (new genetic algorithm (NGA)) and compare its performance with random and optimal (exhaustive) algorithms. We perform experiments on a synthetic database with replicated relations, but no horizontal or vertical fragmentation. Network links are assumed to be gigabit ethernet. Comparisons with optimal results show that our NGA formulation performs only 20% of the optimal results and we have achieved 50% improvement over a previous GA-based algorithm.
A distributed database system named ''Data-Free-Way (DFW)'' is under development by a cooperation among three Japanese national research organizations to support the creation of advanced nuclear materi...
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A distributed database system named ''Data-Free-Way (DFW)'' is under development by a cooperation among three Japanese national research organizations to support the creation of advanced nuclear materials. The development of DFW started in 1990 as a five-year program with a support from Science and Technology Agency of Japan. Before starting the program, a preliminary survey of both domestic and foreign databases of nuclear materials had been made for two years. Then, subjects for the construction of DFW were extracted. To meet the subjects, the development and construction programs were established. The DFW is constructed on the computer network which connects engineering workstations in the separate organizations. A relational database management system is used, a distributed material database is equipped on the hardware with specially designed common data structure. Data storage has been carried out continuously in each organization. The equipment of useful user-interface systems, such as retrieval, data entry and process supporting and image data handling systems, have also been constructed to make it friendly for users. The collection of nuclear material data from three research organizations and its mutual usage have become possible by the construction of DFW.
The goal of checkpointing in database management systems is to save database states on a separate secure device so that the database can be recovered when errors and failures occur. Recent study shows the possibility ...
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The goal of checkpointing in database management systems is to save database states on a separate secure device so that the database can be recovered when errors and failures occur. Recent study shows the possibility of a checkpointing mechanism that does not interfere with the transaction processing, and yet achieves the global consistency of the checkpoints. The motivation of non-interfering checkpointing is to improve the system availability. Although the property of non-interference is highly desirable in many applications of distributed database systems, where restricting transaction activity during the checkpointing operation is not feasible, it makes checkpointing complicated and increases the workload of the system. In this paper, we study the practicality of a non-interfering checkpointing algorithm by analyzing the extra workload of the system
A Bloom filter based semijoin algorithm for distributed database systems is presented. This algorithm reduces communications costs to process a distributed natural join as much as possible with a filter approach. An o...
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A Bloom filter based semijoin algorithm for distributed database systems is presented. This algorithm reduces communications costs to process a distributed natural join as much as possible with a filter approach. An optimal filter is developed in pieces. Filter information is used both to recognize when the semijoin will cease to be effective and to optimally process the semijoin. An ineffective semijoin will be quickly and cheaply recognized. An effective semijoin will use all of the transmitted bits optimally. No other known method can achieve lower communications cost. [ABSTRACT FROM AUTHOR]
In this paper, a net model for decentralized control of user accesses to a distributed database is proposed. It is developed in detail for the restricted case of updating distributed copies of a single database. Predi...
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In this paper, a net model for decentralized control of user accesses to a distributed database is proposed. It is developed in detail for the restricted case of updating distributed copies of a single database. Predicate/transition-nets, a first-order extension of Petri nets, are shown to provide suitable means for concise representation of complex decentralized systems and for their rigorous formal analysis. It will be demonstrated in the present paper how these net models can be constructed and interpreted in a quite natural manner and how they can be analyzed by linear algebraic methods. By this, it will be shown that the modeled distributed database system is deadlock-free and guarantees a consistent database as well as a fair and effective service to the users.
Different database fragmentation and allocation strategies have been proposed to partially replicate data in a partitioned, distributed database (DDB) environment. The replication strategies include database snapshots...
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Different database fragmentation and allocation strategies have been proposed to partially replicate data in a partitioned, distributed database (DDB) environment. The replication strategies include database snapshots, materialized views, and quasi-copies. These strategies are 'static' and do not adapt to the changes in the data usage patterns. Furthermore, they often require expensive update synchronizations to maintain data consistency and do not exploit the knowledge embedded in the query history. This paper describes a machine learning based time invariant fragmentation method (MLTIF) that acquires knowledge about the data usage patterns for each node. Based on this knowledge, MLTIF designs time invariant fragments (TIF) and schedules its allocation and selective update for a specified time period. Simulation is used to compare the effectiveness of the MLTIF approach with that of full replication, materialized views, and non replication strategies. Initial results indicate that for most normal operating conditions, the MLTIF approach can be effective.
In a distributed database system, data replicas are placed at different locations of a network to achieve the high data availability in presence of link failure. Optimal placements of data replicas have been studied e...
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In a distributed database system, data replicas are placed at different locations of a network to achieve the high data availability in presence of link failure. Optimal placements of data replicas have been studied extensively in the literature for various protocol. In this paper, we present a sufficient and necessary condition for optimality of a placement of odd number of data replicas in a ring network with majority voting protocol. As a corollary, we give a proof of a recent conjecture of Hu et al. (manuscript. 1999). Moreover, we also give a simple algorithm to find optimal placements in tree network with majority voting protocol. (C) 2001 Elsevier Science B.V. All rights reserved.
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